title: VCSEL-based, high-speed, in situ TDLAS for in-cylinder water vapor measurements in IC engines.
abstract: We report the first application of a vertical-cavity surfaceemitting laser (VCSEL) for calibration- and sampling-free, high-speed, in situ H2O concentration measurements in IC engines using direct TDLAS (tunable diode laser absorption spectroscopy). Measurements were performed in a single-cylinder research engine operated under motored conditions with a time resolution down to 100 μs (i.e., 1.2 crank angle degrees at 2000 rpm). Signal-to-noise ratios (1σ) up to 29 were achieved, corresponding to a H2O precision of 0.046 vol.% H2O or 39 ppm · m. The modulation frequency dependence of the performance was investigated at different engine operating points in order to quantify the advantages of VCSEL against DFB lasers.
authors.forename: O
authors.initials: O
authors.lastname: Witzel
authors.forename: A
authors.initials: A
authors.lastname: Klein
authors.forename: C
authors.initials: C
authors.lastname: Meffert
authors.forename: S
authors.initials: S
authors.lastname: Wagner
authors.forename: S
authors.initials: S
authors.lastname: Kaiser
authors.forename: C
authors.initials: C
authors.lastname: Schulz
authors.forename: V
authors.initials: V
authors.lastname: Ebert